Turkey’s Premier Recep Tayyip Erdogan, embattled by protests and corruption scandals, faced a crucial popularity test Sunday when over 50 million eligible voters cast their ballots in local elections.

Turkey's Premier Recep Tayyip Erdogan, embattled by protests and corruption scandals, faced a crucial popularity test Sunday when over 50 million eligible voters cast their ballots in local elections.

Hailed as the "sultan" by his loyal followers and labelled a "dictator" by his bitter foes, Erdogan has campaigned for weeks alongside mayoral candidates, turning the vote into a referendum on his 11-year-rule.

The outcome -- especially in the megacity Istanbul and capital Ankara -- will impact his future as he eyes a run for the presidency in August, or changes party rules to seek a fourth term as prime minister next year.

The polls opened first in eastern Turkey at 07:00 am (0500 GMT) and will open in the west at 08:00 am.

More than 50 million voters were to cast their ballots for mayors and local assemblies at almost 200,000 pollings stations, pitting Erdogan's Islamic-rooted Justice and Development party against secular, nationalist and other groups.

To ensure the vote runs smoothly, the authorities have delayed by one day Turkey's switch to summer time.

The past 10 months have spelled crisis for Erdogan, a leader long hailed at home and abroad for driving economic growth and turning the country spanning Europe and Asia into an emerging global player.

But the secular urban middle-class has been alienated since police harshly cracked down on protesters in Istanbul's Gezi Park last June, sparking off weeks of street clashes that left eight people dead and thousands wounded.

The harsh response fuelled a growing perception of an autocratic leader seeking "one-man rule" while falling out with former allies -- especially the influential Pennyslvania-based Muslim cleric Fethullah Gulen, now his declared arch-enemy.

Erdogan has accused Gulen, and his loyalists in the Turkish police force and justice system, of being behind a spate of wiretaps and social media leaks exposing graft and high-level security talks weighing military action in Syria.

The government's response -- especially blocking Twitter and YouTube in the past two weeks -- has sparked a chorus of condemnation from Turkey's NATO allies and human rights groups.

"We will teach a major lesson to Pennyslvania, to those who tapped the telephones," Erdogan vowed on the eve of the polls. "They are traitors ... they are spies ... We will emerge stronger again, God willing!"